Ever since the discovery of the rock, military technology has made it possible to kill from a distance. While rocks remain in use, millennia of design iterations have brought us the laser-guided AGM-114 Hellfire missile, which can be fired by remote control from a MQ-9 Reaper drone by an operator as far away as 1150 miles. Already, thousands of people have been killed in this way. Drone Warfare, by philosopher John Kaag and political scientist Sarah Kreps, invites us to consider the implications of this for politics and domestic accountability, for international law, and for ethics.

First up for consideration is how drones undermine political accountability.

Despite its title, Drone Warfare is not a comprehensive treatment of drone warfare. There is very little discussion of the technical aspects of drones beyond what is necessary in order to understand their uses. With that information briefly established, the book focuses squarely on normative questions about drone warfare. Moreover, the book’s discussion addresses these questions almost exclusively with regard to the United States, the largest and most prolific user of drones. The U.S. is also, the authors hope, in the best position to establish norms and best practices regarding drones by virtue of its military might and international stature.

While drones are still a developing technology, the drone arsenal possessed by the United States already encompasses a wide variety of drone types with a correspondingly extensive range of potential missions. The authors have wisely narrowed their focus to perhaps the most troubling mission, the one most fraught with legal, political, and moral implications: the use of drones to kill suspected terrorists. These attacks can be “targeted killings,” aimed at a known individual, or “signature strikes,” aimed at someone whose behavior fits a “signature” or profile of suspected terrorists.

A recurring frustration I encountered with the book (one no doubt shared by its authors!) was the paucity of detailed, accurate data about drone use. While much of the book’s discussion is therefore unavoidably speculative, the authors do their best to lay out what facts are available about drone strikes on suspected terrorists. The U.S. Department of Defense carries out drone strikes in combat zones (Afghanistan, Iraq, and Libya). Outside of combat zones (chiefly in Pakistan, Yemen, and Somalia) these take place under the aegis of the CIA. The U.S. began using drones to kill suspected terrorists in the aftermath of the September 11th attacks when Congress enacted the Authorization for the Use of Military Force (AUMF), handing the George W. Bush administration extremely open-ended authority to target those who “planned, authorized, committed, or aided the terrorist attacks.” The Obama administration continued and expanded upon the drone policies of its predecessor, conducting more than one hundred drone strikes in Afghanistan alone in 2008 and more still in the following years. Drone strikes outside of combat zones also increased markedly under Obama. Some of those killed have been American citizens, most famously Anwar Al-Awlaki. The AUMF remains in effect, and is now being used to justify operations against groups that did not even exist when it was passed.

With some basic facts briefly established, the authors turn to normative matters. First up for consideration is how drones, which enable governments to engage in covert warfare with minimal risk of loss of life on the part of their service members, undermine political accountability. According to one influential strand of democratic theory (which the authors trace back to Kant’s essay on perpetual peace), the high cost of war in blood and treasure should make leaders who must answer to their citizenry wary of military adventurism. When, thanks to drone use, soldiers rarely come home in body bags, members of the public are not often prompted to care about or even notice military activity half a world away, even if it is ostensibly carried out in their name. Meanwhile, voting against counter-terrorism measures exposes legislators to blame if a terrorist attack happens, but if attacks fail to happen they are rarely in a position to take credit. Thus, neither the public at large nor their elected representatives have much incentive to rein in drone use. Things are no better in the case of the judicial branch, as cases brought against the government after a drone strike has already taken place are unlikely to succeed given the deference courts have traditionally given to national security concerns. Pre-approving strikes would also be problematic. Careful legal deliberations do not mesh well with targeted killings where the window of opportunity to make the attack may be open for only a few minutes. Special drone courts to pre-approve strikes, modeled on Foreign Intelligence Surveillance Act (FISA) courts, are another possibility, but these run the risk of becoming little more than a rubber stamp. (Courts approve virtually all FISA requests.)

The most tightly-argued section of the book concerns international law. One key issue is whether, under the United Nations Charter, U.S. commitments specifying when a recourse to military force is justified (jus ad bellum) are consistent with conducting targeted killings in places where the U.S. is not officially at war. Attempts to justify targeted killings under international law revolve around the idea that they constitute anticipatory self-defense against an imminent threat of terrorist attacks. The AUMF provides some additional support, serving as an analogue to a declaration of war against terrorist groups. The authors reject this line of argument pointing out, first of all, that terrorist groups like Al-Qaeda are non-state actors, and hence not the sort of entities upon which international law sanctions wage war. Second, even in the case of state-sponsored terror groups, the U.S. would still need to be continuously at war with the sponsor to justify military action. Finally, very few actions against terrorists can plausibly be described as anticipatory self-defense against an imminent threat.

The second main question is whether drone use violates the international laws of war concerning the conduct of war once initiated (jus in bello). The two key principles here are distinction and proportionality. “Distinction” is a matter of distinguishing between civilians and military combatants. The signal advantage of drones from the U.S. point of view is that, unlike the indiscriminate destruction wreaked by strategic bombing or artillery barrages, drones are technically capable of targeting even a single individual with a fair degree of precision, thus helping to avoid civilian casualties. The authors argue forcefully, though, that there is a vast gulf between this technical capacity and actually choosing legitimate targets. It is the nature of asymmetrical warfare that potential targets are not always actively engaged in warlike acts, which in any case exist along a continuum from minimal involvement (passing information to militants, say) to wearing a combatant’s uniform and firing on U.S. troops. No amount of precision shooting can take the place of human judgment in selecting legitimate targets in the first place. Even if, as the authors note, more precise strikes are preferable to indiscriminate strategic bombing, that still does not in itself mean the more narrowly-targeted strikes are zeroing in on a target they are justified in hitting.

The other aspect of jus in bello is “proportionality”: whether expected military gains are excessive in light of incidental but foreseeable harm to civilians that may result. The authors helpfully frame their discussion here by looking at the question of whether targeted killings are, in the long run, strategically useful in combatting terrorism. The goal of counterinsurgency operations is ultimately to win hearts and minds. As we saw in Vietnam, body counts are not a good metric for this. Furthermore, the very effort to minimize U.S. casualties by using drones instead of putting troops in harm’s way may cause the U.S. to lose touch with civilian populations and be seen as an oppressive occupier rather than a potential partner in rooting out militants. Thus, while targeted killings are undeniably effective tactically, the authors argue, it is likely that they are worse than useless strategically.

When thanks to drone use soldiers rarely come home in body bags, members of the public are not often prompted to care about or even notice military activity half a world away.

As the authors themselves occasionally note, many of the issues they raise about domestic politics and international law are not uniquely attributable to drones. Their critique broadly implicates U.S. counter-terrorism policy in the 21st century more broadly. Nevertheless, even if drones are more a symptom than a cause, they are a symptom that aggravates the severity of the underlying disease and weakens the body politic’s resistance to it.

The final chapter before the book’s conclusion concerns the ethical implications of targeted killings and signature strikes. While the chapter opens with the claim that “even in a world fraught with ambiguity, there are certain acts . . . that should be prohibited,” the authors self-consciously avoid arguing about which uses of drones, specifically, should be morally prohibited. They stress that evaluating such questions requires the use of human judgment, and that therefore “we did not write this section on the ethics of war and peace and the moral hazard of military technologies in a manner appropriate to robots: input decision procedure, output decision, and correlated action.” This is fair enough, but while the authors are at pains to point out an urgent need for ethical reflection, they do not do much to identify even which qualitative factors would have salience in making such determinations. Instead, the discussion centers largely on more general issues about modern technology than on matters specific to drones and targeted killings.

The second question is whether drone use violates international laws of war concerning the conduct of war once initiated (jus in bello).

For example, the authors claim that drone operators have an unprecedented amount of “leisure” in Thomas Hobbes’ rather unusual sense of “freedom from constant threat of death.” They argue that operators should use this psychological space to reflect on the moral hazards involved in what they do, as they can kill without suffering the usual consequences that attend doing so. But a few pages later the authors mention how nearly 30% of drone operators experience burnout, which the military defines as “an existential crisis.” Killing a named individual whom you can observe in real time is much more intimate and fraught than firing an artillery shell at or dropping a bomb on anonymous grid coordinates. It seems likely that, if anything, operating a drone engenders more stress and less opportunity for calm reflection than many other well-established military technologies.

This broadening of the argument to issues that are not exclusive to drones recurs in other parts of the chapter, despite an ostensibly narrow focus on targeted killings. The authors, invoking Marcuse’s critique of technological rationality, assert that before we can grapple with specific issues about drones, we must take account of the wide-ranging effects of modern technology on the way we think about, among other things, warfare. Another section draws on Hannah Arendt’s concept of the “banality of evil” to argue that citizens who allow undeclared warfare undertaken in their name to become normalized are complicit in it in ways that they rarely acknowledge. Topics like these are important, but doing more than gesturing at them seems beyond the ambit the authors set in the rest of the book.

We do get a relatively detailed examination of the somewhat outré question of whether using drones might, in some circumstances, be morally obligatory (the authors, unsurprisingly, make a case for “no”), but almost no examination of the far more pressing question of the circumstances, if any, in which targeted killings and/or signature strikes might be morally permissible. A blanket prohibition on assassinations would not be a morally eccentric view, but the authors stress that they are pragmatists and not absolutists, which at least strongly suggests there are at least some cases in which they would countenance the kind of drone strikes they take as their subject in this book. With so much about drone warfare shrouded in secrecy, a real-life case is probably too much to ask for, but I would like to have seen if there we was even an idealized scenario in which the authors would be willing to countenance a targeted killing. (Perhaps on a known terrorist about to trigger a nuclear bomb?)

The book concludes with a slate of sensible recommendations: re-evaluating the AUMF, working towards international agreements about best practices for using drones, and limiting the proliferation of armed drones. Unfortunately, U.S. leadership in these areas seems less likely than it did when the book was published in 2014. This does not, however, diminish the timeliness and urgency of this stimulating book. Kreps and Kaag do a good job of highlighting key issues, even if they are sometimes less forthcoming with firm conclusions than one might like.